1. Field of the Invention
The present invention relates to an alignment system used for overlaying or registering uptake patterns displayed by Single Emission Photon Tomography with specific underlying anatomy by Computer Aided Tomography and/or Magnetic Resonance. The alignment system creates a set of markings in each image which uniquely identifies a cross-section of the imaged object. The invention also relates to a method of using the alignment system.
2. Description of the Related Art
High specificity and the ability to detect occult tumors has made monoclonal antibodies (Mabs) useful as vehicles for targeting diaonostic doses of radionuclides to tumors (Goldenberg et. al., 3 Antibody Immunoconjugates and Radiopharmaceuticals, 151-167 (1990)). Recently, it has been shown that the highest accuracy rates are found for Mabs labeled with I-131, I-123, or Tc-99m (Goldenberg et. al., 3 Antibody Immunoconjugates and Radiopharmaceuticals, 151-167 (1990)). The use of single photon emission tomography (SPECT) for antibody imaging has compelled the investigator to correlate findings of SPECT with computed tomography (CT) and magnetic resonance (MR) images, because although CT and MR images are more accurate than SPECT images they suffer from a lack of physiological information. Correlation of the images is especially useful to identify lesions near the organs, such as liver, kidney, spleen, bladder and major blood vessels where the tumor activity uptake may be shadowed by the uptake of the adjacent organ. Different image registration methods were developed to perform image correlation. A surface fitting method has been described to register head scans (Chen et. al., Important Adv. Oncol., 131-134 (1990). It has the advantage that no specific headholders or positioning need be performed during data acquisition but it requires an expert for identification of regions of interest (ROI) and is not suitable for Mab images, because of the lack of anatomical landmarks. This technique also requires a rigid structure which the skull and to some extent the features of the brain provide more than the abdomen or the torso. Other disadvantages include 1) identified organ used as fiducial is sufficient only for "local" region; 2) requires time consuming contouring; 3) not being a general method, therefore anatomical markers have to be uniquely identified each time; and 4) organ dependence-non-tumor concentration of radiolabel uptake is variable.
Another method has been described to register gastrointestinal and lung carcinoma images (Kramer et. al., 172 Radiology, 861-865 (1989)) and Kramer et. al., 1 Nucl. Med. Bio., 27-42 (1991)). That method uses external and anatomical land- marks. Each landmark from the reference image is cross-correlated with the corresponding landmark from the other image. The differences between the two images are compensated through the warping algorithm which allows for translation, rotation, scale, and skew. Although registered images are accurate this method suffers from the disadvantages which are 1) repeated precise application of external markers and frame is difficult on a "moving" patient; 2) matching a external marker with an anatomical landmark may be problematic; 3) choosing the same pair of points from two images is operator and "movement" dependent; and 4) since only one cross-section is matched from each study, if there is a translation or rotation which is different in another cross-section, they may accumulate interpolation error.
There is thus a need for image alignment system which is machine based and uses external landmarks. In particular, there is a need for an alignment system which is 1) free from motion artifact; 2) organ independent, so concentration of radiolabel uptake in the organs is not a factor; 3) allows for minimum operator interference; 4) can be generally used for every patient; 5) where rotation and translation of the patient is not a problem; and 6) where the alignment system is machine compatible with minimal additional effort needed from the machine operator.